Various resilient hinges, such as those which are used, in particular, for one-piece extruded plastics closing means, are known from the prior art. As a rule, a so-called snap effect is to be achieved in such hinges for plastics closing means. The term `snap effect` designates an automatic opening of the hinge after a specific initial deflection (dead centre) forced upon the hinge system, and an analogous effect during closing, in that the hinge automatically returns into a closed position once it has passed a dead centre. This effect is, basically, brought about by special spring elements. Within the context of such snap effects, the snapping force and the working angle are characteristic quantities. The term `snapping force` designates the resistance of the hinge system to opening or closing. The working angle is defined by the region which the parts of the hinge need to overcome automatically, on the basis of spring action, and is, accordingly, defined by the region between the resting positions of the hinge parts.
In the greater majority of such hinges, the basic principle resides in a pivoting of a cover member about a defined rotational movement axis.
European Patent EP 0 056 469 describes a hinge for a plastics closing means, the rotational axis of which is clearly defined and is formed by a defined principal film hinge interconnecting the cover and the sealing body. The snap effect is achieved by a co-operation with spring arms which are arranged on the side of this principal hinge. In one embodiment, the snap effect is based on the bending of U-shaped intermediate elements, while, in another embodiment, it is based on a bending of wall regions of the sealing members, the sealing cap, as a rule, undergoing a bending in the centre region. In this instance, too, the snap effect is brought about by bending actions about the narrow side.
The hinge arrangements known from the WO 92/13775 or EP 0 331 940 patents use primary bending effects in combination with a rotational axis in order to achieve a spring effect for a snap effect. Because of the available geometric rotational axes, the corresponding closing means open along a substantially circular path. In the constructions mentioned, certain parts protrude beyond the outer contour of the closing means, when the closing means is closed.
U.S. Pat. No. 5,148,912 describes a hinge arrangement for a closing means comprising a closure body and a cap, wherein the closing means has the same circular cross-section as the closure body itself. The cap and the closure body are interconnected via two flexible strap-like connecting arms which are trapezoidal in design. These connecting arms are designed to be flexible and are secured to the closing means and to the closure body by means of thin-film regions. The film hinges of the thin-film regions on the side of the closure body are arranged at an angle relative to each other. When the closing means is viewed from the rear, these film hinges are, of necessity but co-incidentally, arranged in the form of a downwardly open V. The arrangement of the two film hinges on the side of the cap are arranged mirror-symmetrically relative thereto. This hinge does not have a good snap effect, since appropriate spring forces cannot develop.
The known hinge arrangements have various drawbacks. In all known hinges comprising a rotational axis, relative to which taut strips or similar elements are arranged so as to be offset (articulation axis offset), it is necessary for this rotational axis to be arranged beyond the outer contour of the closing means in convex injection-moulded closing means. For technical and aesthetic reasons, however, protruding elements are undesirable. A further drawback resides in that the snap effect cannot be predicted, because of complicated mechanical influences, and, as a rule, results in an inadequate snap effect or, alternatively, to an unacceptable stress of the material. A further drawback is the fact that conventional hinge arrangements permit only unpredictable and inadequate working angles which are frequently only about 100.degree.. In the known basic concepts, it is a particular drawback, because of the unpredictable action, that complicated series of prototypes need to be produced in each case for a new geometry of the closing means desired for design reasons, in order to obtain technically satisfactory closing kinematics. The principal hinge, which is present in conventional closing means, necessitates that the parts of the closing means be disposed in very close proximity to each other in the injection-moulded state. The appropriate injection-moulding die thus has the drawback that the wall thicknesses in this region, due to the necessary connection between the closure bodies, must be designed to be very thin. The resultant cooling and wear-related problems arising have an adverse effect on the cycle time and the service life of the injection-moulding die.
A further restriction of such known hinge arrangements, which may be injection-moulded as a single piece of plastic material, resides in that it is possible to produce systems which have at most one snap effect. In other words, a maximum of two positions of rest on either side of at most one dead centre are achieved for the opening operation of the closing means. These positions of rest are, essentially, the open and the closed state of the closing means. Because of the regularly occurring plastic deformations, the open position of rest does not coincide with the position in the injection-moulded state.
The mechanical effects forming the basis of the functioning of such closing means are essentially bending spring effects. The energy required in order to deform a bending element by bending determines the snap force of the hinge. When an element is subjected to bending to an extent which is relevant for this effect, then the corresponding bending deformations in these elements are considerable, in comparison to its characteristic quantities (e.g. thickness of a bending plate) or the bending springs have a considerable spatial dimension in the unloaded state. In the case of very small closing means or in the case of particular geometries of the closing means (small bending radii in the region of the hinge), it is no longer possible to provide the required functional elements of conventional hinge arrangements, such as principal hinge and taut strips, or they produce inadequate snap effects or unacceptable stresses in respect of the material. In addition, a restriction resides in that the closing means must, of necessity, have a convex outer contour in the region of the hinge.
If the flow of force is observed in various available closing means of plastics material, considerable variations will be detected in identical types of closing means. In many constructions, thin-film regions (film hinges) are exposed to stresses to an extent which is unacceptably high. When a fixed rotational movement axis, in the form of a thin-film region, is preset for a closing means, it is possible to detect considerable coercion in the functionally significant elements, in particular in the film regions. Hinge parts which are, for example, firmly interconnected via a principal film hinge, form a relatively rigid unit, even in the open state. When the closing means, when the hinge is open, is forced to execute a relative movement, with respect to the main container, along the principal hinge, considerable stresses may be introduced into the functionally significant hinge elements as a result of this rigid cap/main container connection, accordingly resulting in a destruction of the closing means.
In all these conventional basic hinge concepts, the path described by the hinge parts relative to each other during opening or closing is, essentially, a circular path which is preset exactly by the principal film hinge. When demands are made with regard to the relative movement of the hinge parts during opening, these cannot be met by such constructions.
Many materials (also injection-moulding plastics materials) manifest an unfavourable behaviour if they are exposed to stress over an extended period. These creep and ageing effects have an adverse effect on the functioning of a closing means. It is thus a drawback that known hinge arrangements do not take this into account, often displaying considerable residual stresses in positions of rest.